Various techniques for implementing artificial lift to increase the flow of liquids from a downhole well are known. Such techniques typically involve inland or offshore wells in which a sub-surface downhole apparatus is deployed in the well using wireline, coiled tubing or umbilical cable arrangements, which connect the downhole apparatus to a well-head. As part of routine maintenance or in order to address fault conditions, the downhole apparatus may need to be retrieved from the well.
One of the challenges faced during retrieval is that there is a risk that the downhole apparatus will become stuck in the well, a situation that may arise due to scaling or debris accumulation and other similar factors. The downhole apparatus is typically deployed in a bore with small levels of clearance and hence, relatively small level of scaling or debris accumulation has the potential to affect retrieval.
When the tensile load that may be applied through the cable line is insufficient to successfully retrieve the downhole apparatus, the downhole apparatus must still be removed from the downhole well using other means. Various fishing tools are available to retrieve the downhole apparatus. However, before a fishing operation is performed, it is imperative that the cable line attached to the downhole apparatus is removed so that the downhole bore is clear to rig up the fishing equipment.
In order to address this situation, it is known to incorporate a weak link design in the coupling between the cable line and the downhole apparatus so that when a tensile load substantially greater than the normal operating load is applied, the cable line may be disengaged from the downhole apparatus.
In the past solutions, such as those known from U.S. Pat. Nos. 5,683,115 and 5,109,921, based on mechanical weak link designs using shear pins were proposed. One of the problems with this solution is that the broken pieces of shear pins or bolts, created during the operation of the weak link, further aggravate the problem of debris accumulation over the downhole apparatus. Moreover, such solutions lacked sufficient precision and reliability of operation. Accordingly, other solutions based on electrical and hydraulic actuation systems have been proposed in recent years. While the recent solutions increase the precision, one disadvantage is that in a fault scenario, if the hydraulic or the electrical actuation of the downhole release mechanism becomes inoperable, successfully fishing out the downhole apparatus becomes extremely difficult and cost prohibitive, if not impossible.
Reliable operation of the weak link is of paramount importance. In the event that the weak link fails to operate in the intended manner and the cable line breaks in the region near the well-head, the problem is exacerbated because the cable line, which is typically thousands of feet in length, slides into and clogs the bore of the downhole well and itself needs to be fished out before a fishing operation to retrieve the downhole apparatus may be performed. The breakage of the cable line near an offshore platform results in the additional problem of a pile of the cable line over the well-head on the sea bed.
In light of the foregoing, there is a need for a reliable releasable locking mechanism to releasably couple a cable line to a downhole apparatus.